The melanin-concentrating hormone (MCH) is a cyclic neuropeptide isolated initially from salmon pituitary gland and later from rat hypothalamus (summarized by Nahon et al., 1992 [PubMed 1572663]). In mammals, MCH perikarya are confined largely to the lateral hypothalamus and zona incerta area with extensive neuronal projections throughout the brain, including the neurohypophysis. The anatomic distribution suggests a neurotransmitter or neuromodulator role for MCH in a broad array of neuronal functions directed toward the regulation of goal-directed behavior, such as food intake, and general arousal. MCH and 2 other putative neuropeptides, NEI and NGE, are encoded by the same precursor and appear colocalized in nerve cells and in many instances within the projections. The precursor is designated pro-melanin-concentrating hormone (PMCH).